1. Field of the Invention
The present invention relates to a method of manufacturing a multi-stage pulley having a plurality of groove sections with which a driving belt is engaged.
2. Description of the Related Art
Concerning the method of manufacturing a multi-stage pulley, for example, Japanese Unexamined Patent Publication No. 63-63544 discloses a method in which a workpiece used for manufacturing a multi-stage pulley is plastically deformed by a groove forming roller in which a plurality of groove forming sections are arranged coaxially and integrally with each other so that the groove sections can be formed.
Each groove section of a multi-stage pulley is formed when a workpiece of the multi-stage pulley is plastically deformed by a groove-forming roller. Therefore, a shearing force is given to an end of the groove forming roller according to the plastic deformation. For the above reasons, there is a high possibility that the groove-forming roller is damaged in the process of forming the grooves by the method disclosed in the above patent publication.
In order to solve the above problems, the present inventors made investigation into a means for successively forming a plurality of grooves at different positions so as to prevent the groove-forming roller from being damaged. As a result of the investigation, it was possible to prevent the groove-forming roller from being damaged, however, the following new problems were encountered. Unlike the case described in the above patent publication in which formation of a plurality of grooves is conducted by a groove-forming roller having a plurality of groove-forming sections which are coaxially arranged, it is impossible to simultaneously form the plurality of groove sections by the means which was attempted in the investigation. Accordingly, a groove, which is adjacent to a groove being formed now, is deformed in the process of groove formation.
Due to the foregoing, the yield of manufacturing the multi-stage pulleys is deteriorated, and the manufacturing cost is raised.
In view of the above circumstances, the present invention has been accomplished. It is an object of the present invention to provide a method of manufacturing a multi-stage pulley by which the manufacturing cost can be reduced without coaxially arranging a plurality of groove forming sections.